Reaction product of gallic acid and a soluble tungsten compound and a process of making it



Patented Apr. 27, 1937 REACTION PRODUCT OF GALLIC ACID AND A SOLUBLE TUNGSTEN COMPOUND AND- A PROCESS OF MAKING IT Aladar Pacz, Weehawken, N. J.

No Drawing.

Application November 23, 1933,

Serial No. 699,430. In Germany November 24,

Claims.

The presentinvention deals with the manufacture of highly plastic tungsten compounds from which wires for electric illuminating purposes can be. produced in a particularly advantageous way,

5 while it is also possible to make alloys, hard tools and hollow bars from the compound. The plastic tungsten. compounds made according to the invention are particularly suitable for the manufacture of wires in the presence of large quantities of second class conductors with high electron emissivity, such as thorium oxide and the like. r i

It has always been attempted to use as the starting material for the production of such objects, tungsten compounds which have a certain plasticity. For instance, a method has been described in my United States Patent No. 1,071,568 for producing tungsten compounds of the mentioned type by precipitation of organic tungsten 20 compounds from solutions of ammonium tungstate and gallic acid by means of sulphuric acid. The tungsten compounds precipitated according to this method, and particularly by means of the concentrations of the solutions indicated in this patent, have a certain plasticity sufficient for the production of wires. However, the plasticity is not sufilcient to make it possible to add, for instance, finely pulverized materials in reasonable quantities.

30 It was found that it is possible to produce organic tungsten compounds with a considerably higher plasticity and binding capacity when the concentrations or theratio of the soluble tungsten compounds and the gallic acid are changed 0 considerably. Contrary to the indications given in the patent, where the ratio of the gallic acid and the ammonium tungstate is approximately 1: 4 or 1: 5, the ratio between the gallic acid and the soluble tungstates is selected according to the invention, at least as 1: 2. Consequently, the percentage of gallic'acid in the solution as compared to the soluble tungstic acid compound will be considerably greater than in the known method.

According to tests made up to date, that ratio proved to be the most favorable which gave approximately the same percentage of gallic acid to a certain amount of tungstic acid compound. However, slightly larger ratios have also given favorable results. The formulas of the organic tungsten compounds which are obtained by the method according to the invention may be left out of consideration. However, it has been proved that they are of a type differing from the compounds obtained according to the previously described method, as they have a considerably higher plasticity and binding capacity. It is self-evident that the invention does not only cover a method in which one sharply defined organic tungsten compound is obtained; it is rather possible that the tungsten compounds precipitated at the various concentrations will also be different. However, as long as. the concentrations are selected within the limits indicated, highly plastic organic tungsten compounds will be produced. Small differences in these compounds can be utilized to advantageby adapting them to the various purposes for which they are to be used.

The invention will be explained in greater detail with the aid of an example. 12 grams of gallic acid are dissolved and boiled in liter of water. To this solution 12 grams of very finely pulverized ammonium'tungstate are added. Contrary to the. previously known methods, an organic tungsten compound is immediately formed, that is, without any further addition of acid; this compound is present as a precipitate. This compound can be filtered and proves to have extremely high plastic properties. To the remaining solution, approximately 5 cu. cm. of diluted hydrochloric acid can be added, whereupon the remainder of the tungsten, which is approximately of the total tungsten, will be precipitated in the form of a similarly highly plastic organic compound. In practice both operations can be combined, in which case the deposits can be filtered together. The precipitate is heated carefully in order to eliminate the greatest part of the water present therein.

Instead of ammonium tungstate, it is also possible to use other soluble compounds of tungstic acid, although the ammonium tungstate has proved to be the most suitable because of the high 7 volatility'of the ammonium radical. The concentration of the gallic acid solution may also be changed within narrow limits as long as the ratio between the gallic acid and the tungstate remains the same.

The organic tungsten compound obtained in this manner can be used for the manufacture of a large number of tungsten products. For instance, tungsten wires for illuminating purposes can be made by mixing finely pulverized tungsten with a suitable quantity of the organic tungsten compound, which was obtained according to the invention and which has a considerably higher plasticity than the known tungsten compounds. Even when rather large amounts of tungsten powder are added (more than 100 grams can be used in connection with the above mentioned quantities) a mass is obtained which is so plastic that it can be formed into fine wires without difficulties, and even at low pressure through the ordinary metal nozzles or glass nozzles. It is not only possible to make wires with this compound but it is also possible to produce bars that are hammered and drawn, or even tubes or hollow bars.

Besides the addition of finely pulverized tungsten, it is also possible to add other metals in the pulverized state, depending on theupurpose for which the product is to be used; for instance,

molybdenum, tantalum, thorium or the like may be added.

For the radio industry, it is possible without difficulty to add oxides of zirconium or thorium as conductors of the second class to the finely divided metal which serves as a conductor of the first class. It was found that the plasticity and binding capacity of the organic tungsten compound produced according to the invention is so high that the quantity of such oxides could be increased up to 30% whereby the properties of the wires or bars could be increased considerably. Such wires have approximately 10 times the resistance of pure tungsten and have a high electron emissivity, even at low temperatures.

The produced wires, bars or tubes are sintered in the customary manner in an inert atmosphere or in hydrogen by means of an electric current.

The organic tungsten compound or compounds produced in this manner are also suitable for the manufacture of hard metals; in this case,

' it is particularly advantageous if the binding medium adds simultaneously tungsten and an in creased percentage of carbon so that carbonization will take place at the same time as the sintering.

A possible method of procedure in this .case is to mix the binding medium with the individual components of the hard metal to be produced, consequently to mix it with metallic tungsten, carbon in the form of soot, and with an auxiliary metal with a low melting point, such as cobalt or other metals of the iron group. The mixture is-then subjected to heat, on the one hand in order to decompose the organic tungsten compound, and on the other hand to liberate the tungsten introduced by the compound in the finest possible division. However, it is also possible to mix finished tungsten carbide with the organic tungsten compound and the auxiliary metal, in which case the liberated carbon will 5 cause the auxiliary metal tobe carbonized upon the subsequent heating. In that manner a large number of possible combinations can be found in the method of operation, which in general can be adapted to the known methods for the production of hard metals but which individually have special advantages, as the tungsten compound produced according to the invention has a very high binding capacity for the added pulverized metals and as both the tungsten in the finest division and also the carbon are liberated when this compound is decomposed, while the other components of the compound escape in the volatile state.

Another valuable feature of this invention is that the organic tungsten compounds may be mixed with carbon not only in the form of soot or finely divided carbon but carbon in other forms, such as activated carbon. The mixture may then be subjected to heat and will yield activated carbon with improved properties. By

'means of these organic compounds activated car- 1:2, whereby a highly plastic, organic, tungsten product is produced, which has the property of causing a relatively large quantity of finely divided substances to be highly plastic.

2. The method of producing a binder for pulverulent materials having a relatively high plasticity and binding capacity, which comprises forming a reaction product from substantially equal amounts of gallic acid and a soluble tungstate salt, whereby a highly plastic,organic, tungsten product is produced, which has the property of causing a relatively large quantity of finely divided metallic substances to be highly plastic.

3. The method of producing a highly plastic reaction product, which comprises converting soluble tungstic acid compounds and gallic acid, in which the ratio of the gallic acid to the soluble tungstic acid compounds is at least 1:2, into a reaction product and completing the precipitation of the reaction product with the addition of a relatively small amount of mineral acid, whereby highly plastic tungsten compounds are produced, which are capable of combining with relatively large amounts of finely divided substances to form a plastic mixture which can be readily shaped at low pressures.

4. As a new product, a highly plastic reaction product of gallic acid and asoluble tungstate compound in a proportion of gallic acid in excess of one part gallic acid to two parts tungstate compound, said product being highly plastic and having the property of acting as a binder for a relatively large quantity of finely divided substances, and rendering the mixture sufliciently plastic so that it can be readily shaped at low pressures.

5. As a new product, a highly plastic reaction product of gallic acid and a soluble tungstate compound in substantially. equal proportions of gallic acid and tungstate compound, said product being highly plastic and having the property of acting as a binder for a relatively large quantity of finely divided metallic and non-metallic substances.

' ALADAR PACZ. 

